1. Field of the Invention
The invention relates to an ink ejecting apparatus.
2. Description of the Related Art
Conventional impact printers are now being replaced by nonimpact printers and the market for the nonimpact printers is expanding. As one type of nonimpact printers, there is known an ink ejecting printer which is simplest in principle and can easily effect multi-scale or color printing. Of all the types of ink ejecting printers, a drop-on-demand type ink ejecting printer capable of ejecting ink droplets at a required time only in printing has rapidly spread owing to its good ejecting efficiency and its low operating cost.
As typical examples of such a drop-on-demand type ink ejecting printer, there are what is known a Kyser type as disclosed in U.S. Pat. No. 3,946,398 and a thermal ejecting type as disclosed in U.S. Pat. No. 4,723,129, for example. However, the former is hard to reduce in size, and the latter is required to have a high heat resistance of the ink because the ink undergoes a high temperature. Thus, both types have very severe problems.
To solve the above problems at the same time, there has been newly proposed a shear mode type as disclosed in U.S. Pat. No. 4,879,568.
FIGS. 13A and 13B show such a shear mode type ink ejecting apparatus of the related art. Referring to FIG. 13A, reference numeral 500 generally denotes a shear mode type ink ejecting apparatus composed of a base wall 601, a top wall 602, and a plurality of shear mode actuator walls 603 extending between the base wall 601 and the top wall 602. Each actuator wall 603 is composed of a lower wall part 607, bonded to the bottom wall 601 and polarized in a direction shown by an arrow 611, and an upper wall part 605, bonded to the top wall 602 and polarized in a direction shown by an arrow 609. The actuator walls 603 are arranged in pairs to define ink channels 613 therebetween. There are defined spaces 615, narrower than the ink channels 613, between successive pairs of the actuator walls 603 which define the ink channels 613.
Referring to FIG. 13B, a nozzle plate 617 having a plurality of nozzles 618 is fixed to one end of each ink channel 613, and electrodes 619,621 are each provided as metallized layers on both side surfaces of each actuator wall 603. The electrodes 621 are on upper wall part 605 and the electrodes 619 are on lower wall part 607. The electrodes 619,621 are covered with insulating layers (not shown) for insulation from ink. The electrodes 619,621, disposed in the spaces 615, are connected to a ground 623, whereas the electrodes 619,621 disposed in the ink channels 613 are connected to a silicon chip 625 which provides actuator driving circuits.
The ink ejecting apparatus 600 is manufactured in the following manner. First, a piezoelectric ceramics layer polarized in the direction 611 is bonded to the bottom wall 601, and another piezoelectric ceramics layer polarized in the direction 609 is bonded to the top wall 602. The thickness of each piezoelectric ceramics layer is equal to the height of each lower wall part 607 and the height of each upper wall part 605. Parallel grooves are next formed on each piezoelectric ceramics layer by rotation of diamond cutting disks, for example, thereby forming the lower wall parts 607 and the upper wall parts 605. The electrodes 619 are next formed on the opposite side surfaces of the lower wall parts 607 by vapor deposition, and the insulating layer is then provided on the electrodes 619. Similarly, the electrodes 621 and the insulating layer are provided on the opposite side surfaces of the upper wall parts 605.
Lower ends of the upper wall parts 605 and upper ends of the lower wall parts 607 are bonded together, respectively, to define the ink channels 613 and the spaces 615. Then, the nozzle plate 617, through which the nozzles 618 have been formed, is bonded to one end of each of the ink channels 613 and the spaces 615 in such a manner that the nozzles 618 correspond to the ink channels 613, respectively. Further, the other end of each ink channel 613 is connected to the silicon chip 625, whereas the other end of each space 615 is connected to the ground 623.
In operation, when a voltage is applied from the silicon chip 625 to the electrodes 619 and 621 in each ink channel 613, each actuator wall 603 is deformed by a piezoelectric shear thickness effect in such a direction as to increase the volume of the ink channel 613. After a given period of time, the application of the voltage is stopped to restore an original volume of the ink channel 613 in its free condition from the increased volume. As a result, pressure is generated in the ink stored in the ink channel 613 to thereby eject droplets of the ink from the nozzle 618 corresponding to the ink channel 613.
In the ink ejecting apparatus 600 mentioned above, however, the upper ends of the lower wall parts 607 bonded to the bottom wall 601 are bonded to the lower ends of the upper wall parts 605 bonded to the top wall 602. Accordingly, in the process of bonding the upper wall parts 607 and the lower wall parts 605 together, it is very difficult to align both wall parts 607 and 605 requiring a great deal of time thereby reducing the effectiveness of mass production. Furthermore, each actuator wall 603 includes three bonding portions. Accordingly, when each actuator wall 603 is deformed, adhesive layers present at these bonding portions are deformed in a direction reversed to the direction of deformation of the upper wall part 605 and the lower wall part 607 constituting the actuator wall 603, causing a large energy loss at the bonding portions.
Further, in the ink ejecting apparatus 600 described above, the electrodes 619 and 621 disposed in the spaces 615 are connected to a ground 623, whereas the electrodes 619 and 621 disposed in the ink channels 613 are connected to a silicon chip 625 which provides an actuator for the driving circuits. However, a specific structure or method for the electric connection is not disclosed in the above-mentioned references. For example, if the ink ejecting apparatus 600 has fifty ink channels 613, fifty-one air channels 615 are required and it has one hundred and one electric connecting points between the electrodes 619 and 621 which have a quite a small pitch therebetween. Therefore, the electric connections between the electrodes 619 and 621 are difficult and therefore it takes time for the electric connecting process which results in a further reduction in the ability to mass produce.